1) You would observe the below Syslog Messages for FPC:

[Mon Sep 16 09:07:04.865 LOG: Err] 0x002ba6ff, 0x00151243    0x002b821f, 0x0000aaaa    

[Mon Sep 16 09:07:04.867 LOG: Err] 0x002b821f, 0x00000104 WR   0x002b821f, 0x00000104    

[Mon Sep 16 09:07:04.868 LOG: Err] 0x002b821f, 0x0000aaaa WR                  

[Mon Sep 16 09:07:04.868 LOG: Err] hmc_eri_config_complete, eri 63 ext_req error code 1000

[Mon Sep 16 09:07:04.868 LOG: Err] micron_hmc_bringup_post, eri init_continue ext_req read error

[Mon Sep 16 09:07:04.868 LOG: Err] hmc_asic_bringup_post HMC asic 9 post bringup failed

[Mon Sep 16 09:07:04.868 LOG: Err] hmm_hmc_asics_bringup: HMC asic 9 post bringup failed

[Mon Sep 16 09:07:04.868 LOG: Err] hmm_hmc_asics_bringup: HMC asic 9 fatal error after init_continue check done 3797

[Mon Sep 16 09:07:04.868 LOG: Err] hmm_hmc_asics_bringup: HMC asic 9 bringup failed. 

[Mon Sep 16 09:07:04.868 LOG: Err] hmm_table_train_bringup() Failed to post bringup HMC for link training

2) You might see the below messages as well: 

{master:0}

user@device> show log messages | match hmc  

Sep 16 09:36:44

Sep 16 09:07:00 2024 xxxx fpc0 hmc_eri_return_check, INIT_continue vault and link err

Sep 16 09:07:00 2024 xxxx fpc0 Dumping Micron HMC 9 ADDENDUM DUMP 60 entries ...

Sep 16 09:07:00 2024 xxxx fpc0 Dumping Micron HMC 9 DUBUG DUMP 384 entries ...

Sep 16 09:07:00 2024 xxxx fpc0 Dumping Micron HMC 9 FATAL ERR DUMP 3181 entries ...


3) You may observe no alarms or core-dumps.

 

During Junos code upgrade from 15.1 to 17, FPC might go down and wouldn't come up. Log messages shows HMC errors and ASIC bringup failed which indicates that the internal logic in the Hybrid Memory Cube has encountered an error and is failing to recover.

Workaround:
Step 1. Try restarting FPC. 
Step 2. If rebooting FPC does not work, perform a power-cycle.
Step 3. Post power-cycle if you still encounter FPC to be down, go for replacement.